Geology of Interactions of Volcanoes, Snow, and Water:
MOUNT ST. HELENS, WASHINGTON - IMAGES

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Aerial oblique view south of Mount St. Helens and the 1980 dome on 25 March 1982. The dark area is path of a huge snow avalanche, slushflow, and flood, all caused by swift melting and sliding of snowpack induced by small explosive eruption from dome on 19 March.

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View south along west arm of Spirit Lake to the decapitated Mount St. Helens in 1983. Part of the gigantic landslide (debris avalanche) that removed the former summit swept entirely through Spirit Lake (hummock in foreground), causing a tsunami to sweep as high as 250 m (820 ft) above the lake.

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View southeast in November 1987 of Mount St. Helens and the hummocky deposit of the great debris avalanche (in foreground) that removed the pre-eruption summit.

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View southeast of cone of Mount St. Helens in November 1987. During the first minutes of the eruption of 18 May 1980, a great, hot pyroclastic surge swept down the volcano flanks, melting snow and causing huge, destructive floods down adjacent valleys.

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View in 1985 up path of 18 May 1980 catastrophic flood off east-northeast flank of Mount St. Helens. Forest trimlines register the upper limit of flood that overtopped a saddle in the divide (left middleground). Some of the removed trees ended as great logjams, like that visible in right foreground.